Lanthanides and other rare earth elements including yttrium are often added either as a mixture, that is mischmetal, or individually to improve the properties of various steel alloys. Metallurgists have found that rare earths in parts per million quantities improve both the mechanical and plastic properties by acting as strong desulfurizing and deoxidizing agents. Present quality control methods for quantitatively determining the levels of rare earth additives within steel products involve long and laborious separation and concentration steps. Prior attempts to employ X-ray luminescent techniques have been unsuccessful due to the quenching effect imparted by iron and other transition metals.
It is particularly desirable to determine the amount of lanthanides present in alloys that are to be used in nuclear reactors and other applications involving neutron radiation. Various lanthanides, for instance isotopes of neodymium, samarium, europium, gadolinium and dysprosium, have very large cross sections for thermal neutron capture and are therefore objectionable additives to construction materials in facilities where neutron economy is important.
Lanthanide impurities or additives have been included in a large number of hosts other than the transition elements to produce phosphors that have fluorescent characteristics. These phosphors along with sample spectra are presented in "X-Ray Excited Optical Fluorescence Spectrometry. Scope of Application to Trace Rare Earth Determinations" by DeKalb, D'Silva and Fassel, Analytical Chemistry, pp. 1246-1251, Vol. 42, No. 11, Sept. 1970. Effective crystalline hosts are suggested with a wide variety of cations forming simple, binary and ternary oxides. However, none of the host materials presented in the article include transition elements from groups VIIB or VIII, particularly manganese, iron, cobalt and nickel. Moreover, copper from group IB was found to be a noneffective host material in one particular mixture. For purposes of this application, the elements of each group are defined by the periodic table given in Daniels and Alberty, Physical Chemistry, p. 473, 2d. Ed., John Wiley and Sons, Inc., New York, London, 1955, 1961.